Method of preventing voltage breakdown at a surface of a semiconductor substrate of a superjunction semiconductor device

ABSTRACT

A superjunction semiconductor device is provided having at least one column of a first conductivity type and at least one column of a second conductivity type extending from a first main surface of a semiconductor substrate toward a second main surface of the semiconductor substrate opposed to the first main surface. The at least one column of the second conductivity type has a first sidewall surface proximate the at least one column of the first conductivity type and a second sidewall surface opposed to the first sidewall surface. A termination structure is proximate the second sidewall surface of the at least one column of the second conductivity type. The termination structure includes a layer of dielectric of an effective thickness and consumes about 0% of the surface area of the first main surface. Methods for manufacturing superjunction semiconductor devices and for preventing surface breakdown are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 13/432,723, filed Mar. 28, 2012, entitled “Methods forManufacturing Superjunction Semiconductor Device Having a DielectricTermination,” currently pending, which is a divisional application ofU.S. patent application Ser. No. 12/352,276, filed Jan. 12, 2009,entitled “Superjunction Semiconductor Device Having a DielectricTermination and Methods for Manufacturing the Device,” which issued asU.S. Pat. No. 8,159,039 on Apr. 17, 2012 and which claims the benefit ofU.S. Provisional Patent Application No. 61/020,540, filed Jan. 11, 2008,entitled “Superjunction Semiconductor Device Having A DielectricTermination And Methods for Manufacturing The Device,” the entirecontents of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

Embodiments of the present invention relate to a superjunctionsemiconductor device and a method for manufacturing the superjunctionsemiconductor device. In particular, embodiments of the presentinvention relate to a superjunction device having a voltage terminationstructure having a layer of dielectric of an effective thickness.

The success of a controllable semiconductor device at high or ultra-highvoltages is almost entirely determined by a successful implementation ofthe edge termination. Due to the termination of periodic cell structuresat the edges of semiconductor devices, high electric fields appear alongthe edges. Some special arrangements, namely edge terminationtechnologies, are necessary to prevent premature device breakdown alongthe edges. Field plates, multiple field limiting rings (FLR),semi-insulating polycrystalline silicon (SIPOS) as semi-resistive fieldplates, silicon etch contours, and beveled p-n junctions arerepresentative edge termination technologies for high voltagesemiconductor devices. As the voltage ratings of the semiconductordevice increase, the termination region and the ratio between thetermination region and the active region often increases. This resultsin a poorer yield and a higher on-state voltage. In addition, as thevoltage ratings of the semiconductor device increase, more elaborateadditional process steps for fabrication of the termination are requiredin order to prevent premature breakdown and to maintain the terminationeffectiveness.

The invention of superjunction devices by Dr. Xingbi Chen, as disclosedin U.S. Pat. No. 5,216,275, the contents of which are incorporated byreference herein, is a breakthrough and has opened a new scope for thehigh-voltage semiconductor devices. For example, a 600V superjunctionmetal-oxide-semiconductor field-effect-transistor (MOSFET) has onlyabout ⅙^(th)-⅛^(th) of the on-state resistance of the conventional powerMOSFET. To benefit from the superior performance of superjunctiondevices, the high-voltage edge termination is inevitable. Improvementsto the performance of the superjunction devices may be seen in U.S. Pat.No. 6,410,958 (“Usui, et al.”) and U.S. Pat. No. 6,307,246 (“Nitta, etal.”), both of which are incorporated by reference herein, which showimproved voltage breakdown characteristics in superjunction devices.

Prior art superjunction device edge termination designs consume acertain semiconductor area to realize the high breakdown voltage. Forexample, prior art termination regions typically include multiplefield-limiting-rings (FLRs), which are a plurality of outwardly spacedapart doped regions surrounding a peripheral portion of the cell region.An alternate prior art termination region includes a field plate. Inboth examples, to increase the breakdown voltage in the cell, a greaterarea must be consumed by either the FLR structure or the field plate.The area consumed by the edge termination region does not contribute tothe current-handling-capability of the device (which is determined bythe active area size). It has been a goal in the industry to reduce theedge termination size to obtain higher semiconductor wafer output yield.It is desirable to provide an edge termination design that essentiallydoes not consume any portion of the semiconductor wafer/die area.

Additionally, prior art superjunction device edge termination designstypically require a lightly doped epitaxy region (typically n-type,written as n⁻) in the edge termination region to achieve the highbreakdown voltage. The lightly doped epitaxy region has a much lowerdoping concentration than conductivity regions in the active area (suchas the n-columns). Therefore, manufacturers are forced to start with thelightly doped epi-layer or epi-process and convert the epi-layer intohigher doped regions in the active area using different dopingtechniques.

It is desirable to provide an edge termination design without requiringthe lightly doped region, thereby permitting the use of a moderatelydoped epi-layer or epi process and saving half of the doping process foractive area formation. It is further desirable to provide a method formanufacturing superjunction devices with such an edge terminationregion, utilizing known techniques such as plasma etching, reactive ionetching (RIE), inductively coupled plasma (ICP) etching, sputteretching, vapor phase etching, chemical etching, deep RIB, or the like.It is further desirable to provide a method for preventing the prematurebreak down of a superjunction device at the edge portion by using adielectric termination.

BRIEF SUMMARY OF THE INVENTION

Briefly stated, a preferred embodiment of the present inventioncomprises a superjunction semiconductor device. At least one column of afirst conductivity type extends from a first main surface of asemiconductor substrate toward a second main surface of thesemiconductor substrate opposed to the first main surface. At least onecolumn of a second conductivity type extends from the first main surfacetoward the second main surface. The at least one column of the secondconductivity type has a first sidewall surface proximate the at leastone column of the first conductivity type and a second sidewall surfaceopposed to the first sidewall surface. A termination structure isproximate the second sidewall surface of the at least one column of thesecond conductivity type. The termination structure includes a layer ofdielectric of an effective thickness and consumes about 0% of thesurface area of the first main surface.

Another preferred embodiment of the present invention comprises a methodof manufacturing a superjunction semiconductor device. The methodincludes forming at least one column of a first conductivity typeextending from a first main surface of a semiconductor substrate towarda second main surface of the semiconductor substrate opposed to thefirst main surface and forming at least one column of a secondconductivity type extending from the first main surface toward thesecond main surface. The at least one column of the second conductivitytype has a first sidewall surface proximate the at least one column ofthe first conductivity type and a second sidewall surface opposed to thefirst sidewall surface. The method also includes forming a terminationstructure proximate the second sidewall surface of the at least onecolumn of the second conductivity type. The termination structureincludes a layer of dielectric of an effective thickness and consumesabout 0% of the surface area of the first main surface.

Still another preferred embodiment of the present invention comprises amethod of preventing voltage breakdown at a surface of a semiconductorsubstrate of a superjunction semiconductor device. The method includesplacing, proximate an edge portion of the semiconductor substrate, atermination structure having a layer of dielectric of an effectivethickness. The termination structure consumes about 0% of the surfacearea of the surface of the semiconductor substrate.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofpreferred embodiments of the invention, will be better understood whenread in conjunction with the appended drawings. For purposes ofillustrating the invention, there are shown in the drawings embodimentswhich are presently preferred. It should be understood, however, thatthe invention is not limited to the precise arrangements andinstrumentalities shown.

In the drawings:

FIG. 1A is a cross-sectional elevational view of a superjunctionsemiconductor diode having a prior art multiple field limiting ring(FLR) termination structure;

FIG. 1B is a top plan view of the superjunction semiconductor diode ofFIG. 1A;

FIG. 2A is a schematic cross-section view of a superjunctionsemiconductor diode according to an embodiment of the present invention,the semiconductor device having a termination structure that comprisespart of the package;

FIG. 2B is a top plan view of the superjunction semiconductor diode ofFIG. 2A;

FIG. 3A shows a simulation model of a semiconductor diode according topreferred embodiments of the present invention;

FIG. 3B is a partial view of the simulation model of FIG. 3A placed on acoordinate system showing dimensions in units of microns;

FIG. 4A shows results of simulated cathode total currents as a functionof the cathode voltages for the simulation model of FIG. 3A;

FIG. 4B shows simulated electric field strength contours for thesimulation model of FIG. 3A;

FIG. 4C shows simulated electric potential contours for the simulatedmodel of FIG. 3A;

FIG. 5 shows the simulated breakdown voltages of a semiconductor devicehaving an edge termination structure according to an embodiment of thepresent invention, as a function of the relative dielectric constant;

FIG. 6 shows the simulated termination efficiency of an edge terminationstructure according to an embodiment of the present invention, as afunction of the relative dielectric constant;

FIG. 7A is a schematic cross-sectional elevational view of a first basicstructure, fabricated by a trench/implant fabrication process, that canbe used in preferred embodiments of the present invention, the basicstructure having a unit cellular structure, in the order of a trenchfilled with at least one dielectric material, a first column of pconductivity type, a column of n conductivity type, and a second columnof p conductivity type;

FIG. 7B shows one possible top plan view of the first basic structure ofFIG. 7A;

FIG. 8A is a schematic cross-sectional elevational view of a secondbasic structure, fabricated by a trench/implant fabrication process,that can be used in preferred embodiment of the present invention, thebasic structure having a unit cellular structure, in the order of atrench filled with at least one dielectric material, a first column of nconductivity type, a column of p conductivity type, and a second columnof n conductivity type;

FIG. 8B shows one possible top plan view of the second basic structureof FIG. 8A;

FIG. 9A is a schematic cross-sectional elevational view of a basicstructure, for use in preferred embodiments, having a passivation layerand a unit cellular structure in the order of a first column of pconductivity type, a column of n conductivity type, and a second columnof p conductivity type, fabricated by a trench/epi-refill process;

FIG. 9B is a schematic cross-sectional elevational view of a basicstructure, for use in preferred embodiments, having a passivation layerand a unit cellular structure in the order of a first column of nconductivity type, a column of p conductivity type, and a second columnof n conductivity type, fabricated by a trench/epi-refill process;

FIG. 9C is a schematic cross-sectional elevational view of a basicstructure, for use in preferred embodiments, having a passivation layerand a unit cellular structure in the order of a first column of pconductivity type, a column of n conductivity type, and a second columnof p conductivity type, fabricated by a multi-epi/implant process;

FIG. 9D is a schematic cross-sectional elevational view of a basicstructure, for use in preferred embodiments, having a passivation layerand a unit cellular structure in the order of a first column of nconductivity type, a column of p conductivity type, and a second columnof n conductivity type, fabricated by a multi-epi/implant process;

FIG. 10 is a schematic cross-sectional elevational view of a pn diodehaving the basic structure of FIGS. 7A and 7B;

FIG. 11A is a schematic cross-sectional elevational view of a Schottkydiode having the basic structure of FIGS. 7A and 7B in a chip form;

FIG. 11B is a schematic cross-sectional elevational view of a Schottkydiode having the basic structure of FIGS. 7A and 7B in a packaged form;

FIG. 12A is a schematic cross-sectional elevational view of a powerMOSFET having the basic structure of FIGS. 7A and 7B in a chip form;

FIG. 12B is a schematic cross-sectional elevational view of a powerMOSFET having the basic structure of FIGS. 7A and 7B in a packaged form;

FIG. 13 is a schematic cross-sectional elevational view of a powerMOSFET having the basic structure of FIGS. 8A and 8B;

FIG. 14A is a schematic cross-sectional view of a power MOSFET havingthe basic structure of FIG. 9C in a chip form;

FIG. 14B is a schematic cross-sectional view of a power MOSFET havingthe basic structure of FIG. 9C in a packaged form;

FIG. 15 is a partial cross-sectional elevational view of a siliconsubstrate having a heavily doped n⁺ region and a moderately doped nepitaxial layer with a silicon dioxide layer and a silicon nitridelayer;

FIG. 16 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 15 with a photoresist mask;

FIG. 17 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 16 with open windows;

FIG. 18 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 17 after the photoresist mask isremoved;

FIG. 19 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 18 after trenches are formed;

FIG. 20 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 19 after a sacrificial silicon dioxidelayer is grown on the sidewalls and the bottom of the trenches;

FIG. 21 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 20 after the sacrificial silicon dioxidelayer is subsequently removed, exposing the smoothed surfaces of thesidewalls and bottom of the trenches;

FIG. 22 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 21 after the sidewall surfaces of thetrenches are implanted with a dopant of p conductivity;

FIG. 23 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 22 after a drive-in step;

FIG. 24 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 23 after a thin layer of silicon nitrideis deposited on the sidewalls and the bottoms of the trenches;

FIG. 25 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 24 after the trenches are filled;

FIG. 26 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 25 after a photoresist mask is formed toprotect the top surface of the filled trenches;

FIG. 27 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 26 after the top layer of refillmaterial is etched by oxide etching;

FIG. 28 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 27 after photoresist (PR) stripping isperformed to remove the photoresist mask that protects the top surfacesof the filled trenches;

FIG. 29 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 28 after the silicon nitride layer isetched;

FIG. 30 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 29 after the silicon oxide layer 7 inFIG. 29 is etched by oxide wet etching to expose the top surface of thecolumn;

FIG. 31 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 30 after metallization is performed bydepositing the metal layer(s) over the top surface of the substrate;

FIG. 32 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 31 after the edge portions of metallayer(s) over the top surface of the mesas is removed by metal etching;

FIG. 33 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 32 after a passivation layer is formedover the top surface of the substrate;

FIG. 34 is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 33 after pad openings and scribelineopenings are formed by removing the passivation layer at the appropriatepositions;

FIG. 35A is a partial cross-sectional elevational view of thesemiconductor substrate of FIG. 34 after the mesas at the edge portionsof the substrate are removed by self-aligning silicon etching;

FIG. 35B is a partial top plan view of the active region layout of thesemiconductor substrate of FIG. 35A;

FIG. 36 is a schematic cross-sectional elevational view of a packagedsuperjunction Schottky transistor according to a preferred embodiment ofthe present invention; and

FIG. 37 is partial cross-sectional elevational view of a superjunctionMOSFET according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain terminology is used in the following description for convenienceonly and is not limiting. The words “right”, “left”, “lower”, and“upper” designate directions in the drawing to which reference is made.The words “inwardly” and “outwardly” refer direction toward and awayfrom, respectively, the geometric center of the object described anddesignated parts thereof. The terminology includes the words abovespecifically mentioned, derivatives thereof and words of similar import.Additionally, it must be noted that as used herein and in the appendedclaims, the singular forms “a,” “an,” and “the” include plural referenceunless the context clearly dictates otherwise.

Although any embodiment of the present invention may refer to aparticular conductivity (e.g., p-type or n-type), it will be readilyunderstood by those skilled in the art that p-type conductivity can beswitched with n-type conductivity and vice versa and the device willstill be functionally correct (i.e., a first or second conductivitytype). For example, metal oxide semiconductor field effect transistor(MOSFET)-gated devices and insulated gate bipolar transistors (IGBTs)can be fabricated in an epitaxial wafer with an n-type epitaxial layerover a p⁺ substrate (or visa versa).

An n-type semiconductor includes any semiconductor obtained by n-typedoping process, i.e., by adding an impurity (dopant) to a semiconductor,in order to increase the number of free electrons in the material. Forexample, an n-type semiconductor can be obtained by incorporatingphosphorus (P), arsenic (As), or antimony (Sb), into silicon. The n-typesemiconductor can be heavily doped (n⁺), very heavily doped (n⁺⁺),lightly doped (n⁻), or very lightly doped (n⁻⁻). Heavier doping of ann-type semiconductor results in a higher carrier concentration.

A p-type semiconductor includes any semiconductor obtained by p-typedoping process, i.e., by adding an impurity (dopant) to a semiconductor,in order to increase the number of free holes in the material. Forexample, a p-type semiconductor can be obtained by incorporating boron(B) or aluminum (Al) into silicon. The p-type semiconductor can beheavily doped (p⁺), very heavily doped (p⁺⁺), lightly doped (p⁻), orvery lightly doped (p⁻⁻). Heavier doping of a p-type semiconductorresults in a higher carrier concentration.

Doping in accordance with various embodiments of the present inventioncan be carried out using any method or equipment known or to bedeveloped for imparting impurities of either n-type or p-type intoanother material, including, for example, ion implantation and in-situvapor deposition techniques.

As used herein, the term “termination structure” refers to a structureused to realize breakdown voltage close to ideal breakdown voltage at asurface of a semiconductor substrate. According to embodiments of thepresent invention, the termination structure includes a layer ofdielectric of an effective thickness and consumes about 0% of thesurface area of the surface. At a peripheral region of the semiconductorsubstrate, most, if not all, of the upper surface potential/voltagetransition occurs across the dielectric material(s) outside of thesemiconductor substrate, instead of across the edge of the semiconductorsubstrate, as occurs in traditional termination structures. Dielectricssuitable for termination structure formation according to embodiments ofthe present invention include, but are not limited to, air, a nitride,an oxide, a semi-insulating polycrystalline silicon (SIPOS), asilicon-rich nitride, silicon carbide, glass, epoxy, ceramic, siliconegel, molding compound, or a combination thereof.

The “effective thickness” as used herein, refers to that thickness ofthe layer of dielectric that achieves the blocking capacity in asemiconductor device that is being sought by a researcher, designer, ormanufacturer of the semiconductor device. Methods are known in the artfor modeling, designing, and testing the effective thickness of thelayer of dielectric to be used for the instant semiconductor device. Forexample, the electric field contour and electrostatic potential contourfor the instant semiconductor device can be simulated and used todetermine the effective thickness.

As used herein, the term “terminal structure” or “edge termination”refers to a structure that contains any one or more of the structuresinvolved in a terminal for a semiconductor device. The “terminalstructure” can be, for example, an electrode that is connected to thesemiconductor device, such as a gate electrode, a source electrode, or adrain electrode. The “terminal structure” can also be, for example, adoped region in the semiconductor substrate that is in close proximityor adjacent to an electrode connected to the semiconductor device.Examples of such doped regions, include, but are not limited to, a bodyregion, a body contact region, and a source region. The “terminalstructure” can be a combination of any one or more of the electrodes andthe doped regions. In one embodiment of the present invention, the“terminal structure” comprises a gate electrode, a body region, a bodycontact region, a source region and a source electrode.

The device according to embodiments of the present invention can embodyeither a cellular design (wherein the body regions are a plurality ofcellular regions) or a single body design (where the body regionincludes a single region formed in an elongated pattern, typically aserpentine pattern). Although the device will be described as a cellulardesign throughout the following description for ease of understanding,it is understood that embodiments of the present invention encompassboth a cellular design and a single body design. By way of example, adevice according to embodiments of the present invention is among manysuch devices integrated with logic and/or other components into asemiconductor chip as part of a power integrated circuit. Alternatively,a device according to embodiments of the present invention is among manysuch devices integrated together to form a discrete transistor device.

As used herein, the term “high voltage semiconductor device” refers to asemiconductor device that is able to sustain high reverse-bias voltagein the off-state, and carry a large amount of current and yield lowvoltage in the on-state. A high voltage semiconductor device canaccommodate a higher current density, higher power dissipation and/orhigher reverse breakdown voltage than a regular semiconductor device.

As used herein, the term “power semiconductor device” refers to asemiconductor device that is able to carry a larger amount of energy. Apower semiconductor device typically is able to support a largerreverse-bias voltage in the off-state. A power semiconductor device canbe a high voltage semiconductor device. However, a power semiconductordevice can also be a low voltage device, such as an integrated powerdevice. The term “power semiconductor device” includes, but is notlimited to, a high voltage discrete device, a low voltage discretedevice, a high voltage integrated circuit (IC), and a low voltage IC.Power devices can be used as switches or rectifiers in power electroniccircuits, such as switch mode power supplies. Examples of powersemiconductor devices include, but are not limited to, a superjunctionMOSFET, a superjunction metal-semiconductor field-effect transistor(MESFET), a superjunction Schottky diode, a superjunction insulated-gatebipolar transistor (IGBT), a thyristor, and a superjunction pn diode.

Superjunction semiconductor devices according to preferred embodimentsof the present invention include high voltage semiconductor devices andpower semiconductor devices.

FIGS. 1A and 1B schematically illustrate a superjunction semiconductordevice 100 that has a prior art multiple field limiting ring (FLR)termination. Referring to FIG. 1A, the semiconductor device 100 includesa semiconductor substrate 102 situated on a copper slog of leadframe 104and encapsulated by a package inner layer/underfilling 106. A plasticmolding compound 108 further encapsulates the package inner layer 106and the copper slog of leadframe 104. The semiconductor substrate has anactive region 200, also called the die region, and a surroundingtermination region 300. Referring to FIG. 1B, the termination region 300includes multiple FLRs 302. Each FLR 302 uses the semiconductorsubstrate 102 to support the electric field. The higher the devicevoltage, the larger is the proportion of termination region 300 to theactive region 200. Therefore, the termination region can consume arelatively large amount of the surface area for high voltage devices.

FIGS. 2A and 2B schematically illustrate a superjunction semiconductordevice 400 in accordance with preferred embodiments of the presentinvention. The semiconductor device 400 includes a semiconductorsubstrate 102 situated on a copper slog of leadframe 104 andencapsulated by a package inner layer/underfilling 106. A plasticmolding compound 108 further encapsulates the package innerlayer/underfilling 106 and the copper slog of leadframe 104. Thesemiconductor substrate 102 includes essentially the active region 200,and does not contain the FLR termination structure shown in FIGS. 1A and1B. The dielectric package inner layer/underfilling 106 dissipates thesurface electric field and serves the termination function.

Unlike the prior art multiple FLR termination structure shown in FIGS.1A and 1B, the termination structure according to embodiments of thepresent invention is a layer of dielectric of an effective thickness andconsumes about 0% of the surface area of the semiconductor substrate.

FIGS. 3A and 3B illustrate the generation of a simulation model of asemiconductor device in accordance with embodiments of the presentinvention. Not only is the edge portion of the semiconductor substratereproduced in the simulation model, but the surrounding region ofpackage materials is also included. The structural data shown in FIG. 3Bincludes the typical values for a 500V-rated high-voltage superjunctiondevice design, which is used here as an example to show theeffectiveness of a preferred embodiment of the present invention.

FIGS. 4A, 4B and 4C illustrate the simulation results. FIG. 4A showsthat a superjunction semiconductor device having a termination structureaccording to a preferred embodiment provides a simulated breakdownvoltage of about 605.6 V. FIGS. 4B and 4C demonstrate that when thedevice is at the high voltage of 605.6V, the electric field isdissipated within a 150 μm region around the die, with a margin of aboutseveral tens of microns. Therefore, in preferred embodiments, thetermination structure includes a layer of dielectric with a thickness ofat least about 150 micrometers (μm). Most of the packages have athickness much greater than 150 μm and are therefore adequate to servethe function of a termination structure.

FIG. 5 illustrates the simulated breakdown voltages as a function of therelative dielectric constant of the dielectric material that makes upthe dielectric termination region. The simulated breakdown voltage showslittle change within the range of the dielectric constant from about 1to about 3.4. At dielectric constants above 3.4, there is almost nochange in the breakdown voltage. Therefore, almost any of the variousdielectric materials available can be used to form the dielectrictermination structure. Examples of such dielectric materials include,but are not limited to, air, filling gases (inert gases), vacuum, glass,ceramic, epoxy, and other various underfilling materials and moldingcompound plastics. The dielectric termination can also be formed using acombination of any two or more of the dielectric materials.

FIG. 6 illustrates the simulated termination efficiency as a function ofthe relative dielectric constant. The ideal value of the breakdownvoltage is the breakdown voltage when simulated over a structure withinfinite periodic active regions and no existing termination regions. Ofcourse, there is no infinitely large semiconductor chip. The breakdownvoltage is therefore lowered due to the termination of the activeregion. A deliberately designed termination structure can alleviate thedecrease in breakdown voltage. Thus, the efficiency of a terminationdesign is evaluated by a ratio between the breakdown voltage of theactual device and the ideal breakdown voltage. As shown in FIG. 6, adielectric termination region in accordance with embodiments of thepresent invention has an efficiency between about 80%-86%, depending onthe dielectric constant of the package materials used. Such terminationefficiency is comparable to that of the multiple FLR termination of theprior art.

The dielectric termination structure according to embodiments of thepresent invention dissipates the electric field in a region outside ofthe semiconductor substrate. It consumes approximately 0% of the surfacearea of the semiconductor substrate to achieve a breakdown voltage ofabout 604 V and more than 80% termination efficiency. This is in directcontrast with the multiple FLR termination of the prior art, whichdissipates the electric field in the peripheral region of thesemiconductor substrate outside of the active region, and consumes about150 μm on each side of the semiconductor substrate to realize abreakdown voltage of about 520 V. By using a dielectric terminationstructure according to embodiments of the present invention, thesemiconductor substrate can now be essentially entirely employed as theactive region. This results in a higher yield and a lower on-statevoltage. In addition, as described below, simpler processing steps canbe used for the manufacture of a semiconductor device with thedielectric termination structure.

Referring to FIGS. 7A and 7B, a basic structure manufactured by a trenchfabrication process is shown for use in a preferred embodiment of thepresent invention. The basic structure has a unit cellular structure, inthe order of a trench filled with at least one dielectric material, 113or 114, a first column 118 of p conductivity type, a column 120 of nconductivity type, and a second column 122 of p conductivity type.Filled trenches 114 proximate the peripheral portion of thesemiconductor substrate can function as at least a part of thetermination structure. The termination structure can further include oneor more additional layers of dielectric, such as the package innerlayer/underfilling or molding compound for the device.

Referring to FIGS. 8A and 8B, another basic structure manufactured by atrench fabrication process is shown for use in another preferredembodiment of the present invention. The basic structure has a unitcellular structure, in the order of a trench filled with at least onedielectric material, 213 or 214, a first column 218 of n conductivitytype, a column 220 of p conductivity type, and a second column 222 of nconductivity type. Filled trenches 214 proximate the peripheral portionof the semiconductor substrate can function as at least a part of thetermination structure. The termination structure can further include oneor more additional layers of dielectric, such as the package innerlayer/underfilling or molding compound for the device.

FIGS. 9A-9D illustrate additional examples of basic structures for usein preferred embodiments. These basic structures have a passivationlayer 314 proximate a peripheral portion of the semiconductor substrate.The passivation layer 314 can function as at least a part of thetermination structure. The termination structure can further include oneor more additional layers of dielectric, such as the package innerlayer/underfilling or molding compound for the device. The basicstructure can have a unit cellular structure having a column 320 of nconductivity type and a column 318 of p conductivity type fabricated bya trench-epi-process (FIG. 9A); a column 318 of p conductivity type anda column 320 of n conductivity type, fabricated by a trench-epi-process(FIG. 9B); a column 318 of p conductivity type and a column 320 of nconductivity type, fabricated by a multi-epi-process (FIG. 9C); and acolumn 320 of n conductivity type and a column 318 of p conductivitytype, fabricated by a multi-epi-process (FIG. 9D).

The basic structures described above can be applied to any superjunctionsemiconductor device. Such a superjunction semiconductor device may be asuperjunction MOSFET, a superjunction MESFET, a superjunction Schottkydiode, a superjunction IGBT, a thyristor, a superjunction pn diode, andthe like.

FIGS. 10-12 illustrate a pn diode, a Schottky diode, and a power MOSFETrespectively, having the basic structure as shown in FIGS. 7A and 7B.FIG. 13 illustrates a power MOSFET having a basic structure as shown inFIGS. 8A and 8B. In each of the devices of FIGS. 10-13, a trench filledwith at least one dielectric material 114, 214 proximate the peripheralregion of the semiconductor substrate functions as at least a part ofthe termination structure. Additional voltage termination function isprovided by the package inner layer/underfilling 106 or the moldingcompound 108.

FIGS. 14A and 14B illustrate a power MOSFET having the basic structureas shown in FIG. 9C. The passivation layer 314 proximate the peripheralportion of the semiconductor substrate functions as at least a part ofthe termination structure. Additional voltage termination function isprovided by the package inner layer/underfilling 106 or the moldingcompound 108.

FIGS. 15-36 illustrate a trench type process for manufacturing asuperjunction Schottky diode in accordance with a preferred embodimentof the present invention. A Schottky diode has a metal-semiconductorjunction with rectifying characteristics. A Schottky diode typically hasa very short, if not zero, recovery time in on/off transitions, whichmakes it very favorable for high speed applications. By using thesuperjunction structure described above, the breakdown voltage can besignificantly improved.

Referring to FIG. 15, a silicon substrate 1 includes a heavily doped n⁺region 3 and a lightly doped n epitaxial layer 5. A blocking layer 7 ofsilicon dioxide is either grown or deposited on the top surface of theepitaxial layer. The blocking layer 7 has a desired thickness of betweenabout 100 to about 1,000 Angstroms (Å). A layer of silicon nitride(Si₃N₄) 8 is deposited over the blocking layer 7.

In FIG. 16, the silicon nitride layer 8 is masked by a photoresist mask9 to facilitate etching. In FIG. 17, portions of the silicon nitridelayer 8 and the blocking layer 7 which are not covered by thephotoresist mask 9 are etched by nitride and oxide etching to openspaced apart windows 11 on the layers 7 and 8 for silicon trenches. InFIG. 18, photoresist (PR) stripping is performed to remove thephotoresist mask 9.

Referring to FIG. 19, using techniques known in the art, the epitaxiallayer 5 is etched beneath the windows 11 to form trenches 13 that touchor approach an interface 4 between the heavily doped n⁺ region 3 and theepitaxial layer 5. Each of the trenches 13 is adjacent to and forms anadjoining mesa 15 of the epitaxial layer 5. The trenches 13 and mesas 15form the active region of the semiconductor device. Preferably, theetching is performed by utilizing a known technique such as plasmaetching, RIE, ICP etching, sputter etching, vapor phase etching,chemical etching, deep RIE, or the like. Utilizing ICP etching, trenches13 can be formed having depths of about 40 μm to about 300 μm or evendeeper. Deep ICP etching technology permits deeper trenches 13 with muchstraighter sidewalls. Furthermore, forming deeper trenches 13 that havestraighter sidewalls than conventionally etched or formed trenches, inaddition to other steps in the process, results in a final superjunctiondevice with enhanced avalanche breakdown voltage characteristics ascompared to conventional semiconductor-transistor devices (i.e., theavalanche breakdown voltage can be increased to about 200 to 1200 Voltsor more).

The sidewalls of each trench 13 can be smoothed, if needed, using, forexample, one or more of the following process steps: (i) an isotropicplasma etch may be used to remove a thin layer of silicon (typically100-1000 Angstroms) from the trench surfaces or (ii) a sacrificialsilicon dioxide layer may be grown on the surfaces of the trench andthen removed using an etch such as a buffered oxide etch or a dilutedhydrofluoric (HF) acid etch. In FIG. 20, a sacrificial silicon dioxidelayer 17 is grown on the sidewalls and the bottom of the trenches 13. InFIG. 21, the sacrificial silicon dioxide layer 17 has been subsequentlyremoved, exposing the smoothed surfaces 16 of the sidewalls and bottomof the trenches 13. The use of smoothing techniques can produce smoothtrench surfaces with rounded corners while removing residual stress andunwanted contaminates.

Referring to FIG. 22, the width A and depth B of the trenches 13 areused to determine an implantation angle φ, φ′ (i.e., a first or secondangle of implantation φ, φ′) of ion implants to be performed and arediscussed in detail below. Though not shown clearly, in some embodimentsthe trenches 13 are preferably slightly wider at their tops by about1%-10% than at their bottoms to facilitate the trench fill process whenthe trenches 13 are, for example, to be filled with grown oxide.Consequently, the trenches 13 have a first sidewall surface with apredetermined inclination maintained relative to the first main surfaceand a second sidewall surface with a predetermined inclinationmaintained relative to the first main surface. The inclination of thefirst sidewall surface is about the same as the inclination of thesecond sidewall surface depending on tolerances of the etching process.

In other embodiments, it is desirable to have the sidewalls of thetrenches 13 as vertical as possible (i.e., 0° inclination angle). Whilethe trenches 13 extend from the first main or upper surface of theepitaxial layer 5 toward the heavily doped region 3 to the first depthposition B, the trenches 13 do not necessarily extend all the way to theheavily doped region 3.

Many geometrical arrangements of trenches 13 and mesas 15 (i.e., in planview) are also contemplated without departing from the invention.

Referring to FIG. 22, at a first predetermined angle of implantation φ,without the benefit of a masking step, the mesas 15 are implanted with ap dopant, such as boron (B) (i.e., a dopant having a second conductivityor p conductivity), on the first sidewall surface of the trench 13 at ahigh energy level in the range of about 40 Kilo-electron-volts (KeV) toseveral Mega-eV. Preferably, the energy level is in the range of about200 KeV to 1 MeV, but it should be recognized that the energy levelshould be selected to sufficiently implant the dopant. The firstpredetermined angle of implantation φ, as represented by thick arrows,determined as described above, can be between about 2° and 12° fromvertical and is preferably about 4°. The use of the width A and depth Bof the trenches 13 to determine the first predetermined angle ofimplantation φ ensures that only the sidewalls of the trenches 13 andnot the bottoms of the trenches 13 in the active region are implanted.Consequently, a dopant of the second conductivity type is implanted, ata first predetermined angle of implantation φ, into at least onepre-selected mesa 15 to form at the sidewall surface of the one trench13 a first doped region of the second conductivity type having a dopingconcentration lower than that of the heavily doped region 3. Otherdoping techniques may be utilized, for example, a vapor phasedeposition.

The opposite sides or second sidewalls of the trenches 13 are implantedwith boron at a second predetermined angle of implantation φ′, asrepresented by thick arrows. Similar to the first predetermined angle ofimplantation φ, the second predetermined angle of implantation φ′ can bebetween about −2° and −12° from vertical and preferably at about −4°.Consequently, a dopant of the second conductivity type is implanted, ata second predetermined angle of implantation φ′, into at least onepre-selected mesa 15 to form at the sidewall surface of the one trench13 a second doped region of the second conductivity type having a dopingconcentration lower than that of the heavily doped region 3. Otherdoping techniques may be utilized, for example, a vapor phasedeposition.

In FIG. 23, following implantation of the second p-type implant (FIG.22), a drive-in step (i.e., a diffusion) is performed at a temperatureof up to about 1200° Celsius for up to about 12 hours. After thedrive-in step, the mesas 15 adjacent to two trenches 13 are converted topnp columns 19, each of which comprises p columns 18 and an n column 20.It should be recognized that the temperature and the time thetemperature is maintained are selected to sufficiently drive in theimplanted dopant into the mesas 15. Also shown in FIG. 23, oxidation isalso performed with the drive-in step, which forms a silicon dioxidelayer 21 on the sidewalls and the bottoms of the trenches 13.

In FIG. 24, a thin layer of silicon nitride 23 is deposited on thesilicon dioxide layer 21 on the sidewalls and the bottoms of thetrenches 13. The layer of silicon nitride 23 serves several functions,namely i) balancing the mechanical stress; ii) creating a stop layer forchemical-mechanical-polishing (CMP) or etching; and iii) isolating andprotecting the silicon and silicon oxide in the columns 19 from refillmaterial 25 to be deposited in the trenches 13.

The lining of the trenches with silicon nitride 23 is performed, in thepresent embodiment, using a technique known as low pressure (LP)chemical vapor deposition (CVD) of Tetraethylorthosilicate (TEOS) orsimply “LPTEOS.” Alternatively, a spun-on-glass (SOG) technique or anyother suitable technique may be used to line the trenches 13 with thesilicon nitride 23. Preferably, the silicon nitride 23 is about 100 Å toabout 1,000 Å thick (1 μm=10,000 Å).

Referring to FIG. 25, the trenches 13 are then refilled (filled) by SOGtechnique, typically with an insulating or semi-insulating refill (orfill) material 25, such as a dielectric, a polysilicon, a re-crystalizedpolysilicon, a single crystal silicon, or SIPOS. Preferably, thetrenches 13 are refilled with SIPOS. The amount of oxygen content in theSIPOS is selectively chosen to be between 2% and 80% to improve theelectrical characteristics of the active region. Increasing the amountof oxygen content is desirable for electrical characteristics, butvarying the oxygen content also results in altered material properties.Higher oxygen content SIPOS thermally expands and contracts differentlythan the surrounding silicon which may lead to undesirable fracturing orcracking, especially near the interface of differing materials.Accordingly, the oxygen content of the SIPOS is optimally selected toachieve the most desirable electrical characteristics without anundesirable impact on mechanical properties. Also shown in FIG. 25, atop layer of the fill material 25 is also deposited by the SOG techniqueover the silicon nitride layer 8 on the top surface of the pnp columns19 and the mesas 15 at the edge portions of the substrate 1.

In order to create the device features for a transistor to be formedthereon, the top surface of the pnp columns 19 must be exposed. In someembodiments, planarization by CMP or other techniques known in the artcan be performed so as to sufficiently expose the pnp columns 19 whilepreventing the opening of any internal voids 27 in the fill material 25that may have occurred during the fill process. Preferably, theplanarization is about 1.0-1.5 μm.

FIGS. 26-30 illustrate process steps that may be used to expose the topsurfaces of the pnp columns 19. In FIG. 26, a photoresist mask 29 isformed to protect the filled trenches 13. In FIG. 27, the fill materiallayer 25 is etched by oxide dry etching to remove the fill materiallayer 25 from the areas other than those above the filled trenches 13.In FIG. 28, PR stripping is performed to remove the photoresist mask 29from above the filled trenches 13. In FIG. 29, the silicon nitride layer8 is etched for removal by methods known in the art. In FIG. 30, thesilicon oxide layer 7 is etched for removal by oxide wet etching.

Referring to FIG. 31, using methods known in the field, metallization isperformed to deposit a layer of metal 32 over the top surface of thefilled trenches 13, the pnp columns 19, and the mesas 15 at the edgeportions of the substrate 1. Schottky contact is formed between themetal layer 32 and the top surface of columns 19. Note that only metaland semiconductor contacts capable of rectifying currents are consideredSchottky contacts. Rectifying properties depend on the work function ofthe metal, the band gap of the intrinsic semiconductor, and the type andconcentration of dopants in the semiconductor. Design and formation of aSchottky contact is known to those skilled in the art.

In FIG. 32, the metal layer 32 over the top surface of the mesas 15 atthe edge portions of the substrate 1 is removed by metal etching. InFIG. 33, a passivation layer 33 is formed over the top surface of themesas 15 at the edge portions of the substrate 1 and the remaining metallayer 32, using an appropriate passivation material such as nitride,oxide, phosphosilicate glass (PSG), or undoped silicate glass (USG). Thepassivation layer 33 protects the exposed metallurgical junctions. InFIG. 34, pad openings 34 and scribe line openings 36 are formed byremoving portions of the passivation layer 33 at the appropriatepositions. In FIG. 35A, the mesa 15 at the edge portion of the substrateis removed by self-aligning silicon etching and slight silicon wetetching. This results in a semiconductor device 35 having trenches 13filed with the refill material 25 at the edge portions and the activeregion at the center. The active region including the pnp columns 19 andthe trenches 13 is filled with the refill material 25. A partial topplan view of the active region layout is shown in FIG. 35B, with each ofthe dots representing a pnp column 19 and the striped backgroundrepresenting the refill material 25.

Referring to FIG. 36, the metal layer 32 functions as the gate electrodein a Schottky diode, and bondwire 37 is connected to the gate electrode32. A package inner layer/underfilling 106 comprising a dielectric suchas glass, ceramic, or the like is used to encapsulate the active regionwithin the semiconductor substrate 35. A polymeric molding compound 108is used to further encapsulate the package inner layer/underfilling 106,the semiconductor substrate, and the copper slog of the leadframe 104,which serves as the base frame for the semiconductor substrate 35 andthe package inner layer/underfilling 106.

FIG. 37 is partial cross-sectional elevational view of a cell of aMOSFET superjunction device that can be manufactured by process stepssimilar to those depicted in FIG. 15-36. The MOSFET superjunction devicehas pn-np columns 19 having p columns 18 and n column 20. Each of thepn-np columns 19 is isolated from other neighboring cells by oxide liner21 and silicon nitride liner 23 and the SIPOS or poly refill 25 with therefill void 27. The n⁺ region 3 functions as a drain and the pn-npcolumn 19 is disposed thereon. The device also includes a p body region41 in which there are formed n-source connector regions 43. An oxidelayer 45 separates a gate poly region 47 from the n source connector 43and the p body 41. A metal layer 51 is disposed over the pn-np columns19 and the SIPOS filled trenches 25. A passivation layer 53 is disposedon the metal layer 51 adjacent the pn-np column 19 closest to the edgeof the substrate 3.

As mentioned above, the processes are versatile as the n columns and pcolumns can be exchanged. For the manufacture of p-channel devices thesubstrate is p⁺ and for n-channel devices the substrate is n⁺. Therefill material can be doped or undoped oxide, semi-insulating material(such as SIPOS), SOG, doped or undoped polysilicon (poly), nitride or acombination of materials.

From the foregoing, it can be seen that embodiments of the presentinvention are directed to a superjunction device having a dielectrictermination and methods for manufacturing a superjunction device havingdielectric termination. It will be appreciated by those skilled in theart that changes could be made to the embodiments described abovewithout departing from the broad inventive concept thereof. It isunderstood, therefore, that this invention is not limited to theparticular embodiments disclosed, but it is intended to covermodifications within the spirit and scope of the present invention asdefined by the appended claims.

I claim:
 1. A method of preventing voltage breakdown at a surface of asemiconductor substrate of a superjunction semiconductor device, themethod comprising placing, proximate an edge portion of thesemiconductor substrate, a termination structure comprising a layer ofdielectric of an effective thickness, the termination structureconsuming about 0% of the surface area of the surface of thesemiconductor substrate.
 2. The method of claim 1, wherein thedielectric is one of a nitride, an oxide, an amorphous silicon, asemi-insulating polycrystalline silicon (SIPOS), a silicon-rich nitride,silicon carbide, glass, ceramic, plastic, and a combination thereof.